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<p> The <em>IfcDataTime</em> identifies a particular point in time, expressed by hours, minutes and optional seconds elapsed within a calender day, expressed by year, calender month and day in month. It is expressed by a string value following a particular lexical representation.
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<p>
This lexical representation for <em>IfcDataTime</em> is YYYY-MM-DDThh:mm:ss where "YYYY" represent
the year, "MM" the month and "DD" the day, preceded by an optional leading "-" sign to indicate a
negative year number. If the sign is omitted, "+" is assumed. The letter "T" is the date/time separator 
and "hh", "mm", "ss" represent hour, minute and second respectively. Additional digits can be used to 
increase the precision of fractional seconds if desired i.e the format ss.ss... with any number of 
digits after the decimal point is supported. The fractional seconds part is optional; other parts of 
the lexical form are not optional. To accommodate year values greater than 9999 additional digits can 
be added to the left of this representation. Leading zeros are required if the year value would otherwise 
have fewer than four digits; otherwise they are forbidden. The year 0000 is prohibited.
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<blockquote class="note">
NOTE&nbsp; See extended format representation of <strong>dateTime</strong> as defined in ISO&nbsp;8601. The restrictions defined in XML Schema Part 2 apply.
</blockquote>
<blockquote class="history">HISTORY&nbsp; New type in IFC4.</blockquote>
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